Due to a bug in Vista and Windows 7, users can get the error "User profile services failed the login" when trying to log in. They're unable to get into their user account, but can usually log in to safe mode just fine.
Luckily, this bug has an easy fix.
- Boot into safe mode
- Click on the start button, and type "regedit" into the search bar.
- Hit enter to open regedit.
- Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
- You'll see two "S-1-5...." folders with long names. One of them will end in ".bak"
- Rename the one that does not end in ".bak" to "(long string of numbers).bad" or ".old"
- Remove the ".bak" from the other one.
- With this folder selected, double click RefCount and type 0 and then click OK.
- With this folder selected, double click State and type 0 and then click OK.
- Reboot the machine, and it should be fixed.